The present invention relates to the configurations of optical transmission equipments and optical transport network and the methods of using them. More particularly, the invention relates to an optical switching equipment and an optical transport network which are suitable to processing a plurality of optical signals wavelength-multiplexed with one another and the methods of using them.
In order to achieve higher transmission speed and larger capacity, a study has been made of putting into practice optical switching equipment called an optical add drop multiplexer (referred to as an OADM) or an optical cross connect (referred to as an OXC), which equipment is arranged to not only transmit the wavelength-multiplexed optical signal but also switch the optical signal of a transmission route or path unit, and further of configuring an optical transport network provided with the OADM or the OXC. Herein, the transmission route or the path to be switched is often referred simply to as a route.
The foregoing optical transport network has been requested to have an economical network configuration having a highly reliable long haul transmission capability (such as a transmission without re-generators in the distance of 100 to 300 km). In order to make the network highly reliable, generally, the network has heretofore adopted a redundant configuration such as duplex of the OADM or OXC or duplex of an optical transmission route with protection route. Further, in order to realize the long haul transmission, for compensating a loss of optical signal level, commonly, there has been heretofore used a technique such as addition of an optical amplifier as disclosed in JP-A-5-244098.
The OADM or OXC to be used for configuring the optical transport network is arranged to have a properly selective combination of optical components such as an optical transmitter and receiver, an optical switch, an optical coupler, an optical distributor, an optical amplifier, and a transponder.
However, the existing optical switch brings about a loss of an optical signal in the range of several dB to several tens dB depending on the arrangement of the switch or the set route state. Further, though the optical transmitter and the optical receiver are commonly required to be placed before and after the optical switch, often, it is further requested to add the optical amplifier for adjusting the optical signal level, because the optical transmitter and receiver have a limitation in optical signal output power, receiver sensitivity and dynamic range. Moreover, the redundant configuration adopted for making the network highly reliable needs to have some components such as an optical distributor like an optical coupler and an optical selector like a 2×1 optical switch.
In order to achieve larger capacity on the future optical transport network for coping with the wavelength multiplexing, it is necessary to provide the foregoing optical components such as the optical coupler, the 2×1 optical switch, the transponder, and the optical amplifier for each of the wavelengths to be multiplexed. It means that the use of the redundant configuration like the simple duplex of the OADM or OXC results in making the apparatus larger in size and costly. Since the foregoing optical components (the optical switch, the optical coupler, the 2×1 optical switch, and so forth) bring about a loss of an optical signal in the range of several dB to several tens dB, the optical transport network provided with lots of these components connected in cascade brings about a larger optical signal loss inside the network accordingly. The larger optical loss requires the optical amplifier to be added on the way of the optical transmission route for the purpose of meeting the request of the long haul transmission, thereby making the optical transport network more costly.
In order to configure a highly reliable and economical wavelength-multiplexed optical transport network that is arranged to have a large capacity and make the long haul transmission possible, it is preferable to reduce the optical components in number by properly distributing the redundant configurations of the optical transport network or the equipments configuring the network, thereby reducing the optical signal loss of the network and making the network highly reliable and less costly. That is, it is requested to realize a highly reliable and economically-configured optical switching equipment which is approximate to the long haul transmission by suppressing the configuration redundancy and reducing the optical components in number, assemble these equipments for configuring the optical transport network, and provide the method of using the optical transmission equipment and the optical transport network that meet the foregoing request.